From 61b9f3590405e815d66618acb241700ce3bb71e9 Mon Sep 17 00:00:00 2001
From: Baoshuo <i@baoshuo.ren>
Date: Sun, 29 May 2022 18:44:10 +0800
Subject: [PATCH] =?UTF-8?q?T243086=20=E6=9C=80=E7=AE=80=E5=88=86=E6=95=B0?=
 =?UTF-8?q?=E5=88=97?=
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https://www.luogu.com.cn/record/76645289
---
 Luogu/T243086/T243086.cpp | 43 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 Luogu/T243086/T243086.cpp

diff --git a/Luogu/T243086/T243086.cpp b/Luogu/T243086/T243086.cpp
new file mode 100644
index 00000000..9726471b
--- /dev/null
+++ b/Luogu/T243086/T243086.cpp
@@ -0,0 +1,43 @@
+#include <iostream>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+int n, p, primes[10000005], phi[10000005];
+bool vis[10000005];
+long long ans;
+
+void get_eulers(int n) {
+    phi[1] = 1;
+    for (int i = 2; i <= n; i++) {
+        if (!vis[i]) {
+            primes[p++] = i;
+            phi[i] = i - 1;
+        }
+        for (int j = 0; primes[j] * i <= n; j++) {
+            vis[primes[j] * i] = true;
+            if (i % primes[j] == 0) {
+                phi[primes[j] * i] = phi[i] * primes[j];
+                break;
+            }
+            phi[primes[j] * i] = phi[i] * (primes[j] - 1);
+        }
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+
+    cin >> n;
+
+    get_eulers(n);
+
+    for (int i = 2; i <= n; i++) {
+        ans += phi[i];
+    }
+
+    cout << ans << endl;
+
+    return 0;
+}